The pre-ISO C++ headers (<iostream.h>, <defalloc.h> etc.) are not supported.

For those of you new to ISO C++ (welcome, time travelers!), the ancient pre-ISO headers have new names. The C++ FAQ has a good explanation in What's the difference between <xxx> and <xxx.h> headers?.

Porting between pre-ISO headers and ISO headers is simple: headers like <vector.h> can be replaced with <vector> and a using directive using namespace std; can be put at the global scope. This should be enough to get this code compiling, assuming the other usage is correct.

At this time most of the features of the SGI STL extension have been replaced by standardized libraries. In particular, the unordered_map and unordered_set containers of TR1 and C++ 2011 are suitable replacements for the non-standard hash_map and hash_set containers in the SGI STL.

Header files <hash_map> and <hash_set> moved to <ext/hash_map> and <ext/hash_set>, respectively. At the same time, all types in these files are enclosed in namespace __gnu_cxx. Later versions deprecate these files, and suggest using TR1's <unordered_map> and <unordered_set> instead.

The extensions are no longer in the global or std namespaces, instead they are declared in the __gnu_cxx namespace. For maximum portability, consider defining a namespace alias to use to talk about extensions, e.g.:

      #ifdef __GNUC__
      #if __GNUC__ < 3
	#include <hash_map.h>
	namespace extension { using ::hash_map; }; // inherit globals
      #else
	#include <backward/hash_map>
	#if __GNUC__ == 3 && __GNUC_MINOR__ == 0
	  namespace extension = std;               // GCC 3.0
	#else
	  namespace extension = ::__gnu_cxx;       // GCC 3.1 and later
	#endif
      #endif
      #else      // ...  there are other compilers, right?
	namespace extension = std;
      #endif

      extension::hash_map<int,int> my_map;
      

This is a bit cleaner than defining typedefs for all the instantiations you might need.

The following autoconf tests check for working HP/SGI hash containers.

# AC_HEADER_EXT_HASH_MAP
AC_DEFUN([AC_HEADER_EXT_HASH_MAP], [
  AC_CACHE_CHECK(for ext/hash_map,
  ac_cv_cxx_ext_hash_map,
  [AC_LANG_SAVE
  AC_LANG_CPLUSPLUS
  ac_save_CXXFLAGS="$CXXFLAGS"
  CXXFLAGS="$CXXFLAGS -Werror"
  AC_TRY_COMPILE([#include <ext/hash_map>], [using __gnu_cxx::hash_map;],
  ac_cv_cxx_ext_hash_map=yes, ac_cv_cxx_ext_hash_map=no)
  CXXFLAGS="$ac_save_CXXFLAGS"
  AC_LANG_RESTORE
  ])
  if test "$ac_cv_cxx_ext_hash_map" = yes; then
    AC_DEFINE(HAVE_EXT_HASH_MAP,,[Define if ext/hash_map is present. ])
  fi
])

# AC_HEADER_EXT_HASH_SET
AC_DEFUN([AC_HEADER_EXT_HASH_SET], [
  AC_CACHE_CHECK(for ext/hash_set,
  ac_cv_cxx_ext_hash_set,
  [AC_LANG_SAVE
  AC_LANG_CPLUSPLUS
  ac_save_CXXFLAGS="$CXXFLAGS"
  CXXFLAGS="$CXXFLAGS -Werror"
  AC_TRY_COMPILE([#include <ext/hash_set>], [using __gnu_cxx::hash_set;],
  ac_cv_cxx_ext_hash_set=yes, ac_cv_cxx_ext_hash_set=no)
  CXXFLAGS="$ac_save_CXXFLAGS"
  AC_LANG_RESTORE
  ])
  if test "$ac_cv_cxx_ext_hash_set" = yes; then
    AC_DEFINE(HAVE_EXT_HASH_SET,,[Define if ext/hash_set is present. ])
  fi
])

Historically these flags were used with iostreams to control whether new files are created or not when opening a file stream, similar to the O_CREAT and O_EXCL flags for the open(2) system call. Because iostream modes correspond to fopen(3) modes these flags are not supported. For input streams a new file will not be created anyway, so ios::nocreate is not needed. For output streams, a new file will be created if it does not exist, which is consistent with the behaviour of fopen.

When one of these flags is needed a possible alternative is to attempt to open the file using std::ifstream first to determine whether the file already exists or not. This may not be reliable however, because whether the file exists or not could change between opening the std::istream and re-opening with an output stream. If you need to check for existence and open a file as a single operation then you will need to use OS-specific facilities outside the C++ standard library, such as open(2).

Phil Edwards writes: It was considered and rejected for the ISO standard. Not all environments use file descriptors. Of those that do, not all of them use integers to represent them.

For a portable solution (among systems which use file descriptors), you need to implement a subclass of std::streambuf (or std::basic_streambuf<..>) which opens a file given a descriptor, and then pass an instance of this to the stream-constructor.

An extension is available that implements this. <ext/stdio_filebuf.h> contains a derived class called __gnu_cxx::stdio_filebuf. This class can be constructed from a C FILE* or a file descriptor, and provides the fd() function.

For another example of this, refer to fdstream example by Nicolai Josuttis.

Check for complete library coverage of the C++1998/2003 standard.

# AC_HEADER_STDCXX_98
AC_DEFUN([AC_HEADER_STDCXX_98], [
  AC_CACHE_CHECK(for ISO C++ 98 include files,
  ac_cv_cxx_stdcxx_98,
  [AC_LANG_SAVE
  AC_LANG_CPLUSPLUS
  AC_TRY_COMPILE([
    #include <cassert>
    #include <cctype>
    #include <cerrno>
    #include <cfloat>
    #include <ciso646>
    #include <climits>
    #include <clocale>
    #include <cmath>
    #include <csetjmp>
    #include <csignal>
    #include <cstdarg>
    #include <cstddef>
    #include <cstdio>
    #include <cstdlib>
    #include <cstring>
    #include <ctime>

    #include <algorithm>
    #include <bitset>
    #include <complex>
    #include <deque>
    #include <exception>
    #include <fstream>
    #include <functional>
    #include <iomanip>
    #include <ios>
    #include <iosfwd>
    #include <iostream>
    #include <istream>
    #include <iterator>
    #include <limits>
    #include <list>
    #include <locale>
    #include <map>
    #include <memory>
    #include <new>
    #include <numeric>
    #include <ostream>
    #include <queue>
    #include <set>
    #include <sstream>
    #include <stack>
    #include <stdexcept>
    #include <streambuf>
    #include <string>
    #include <typeinfo>
    #include <utility>
    #include <valarray>
    #include <vector>
  ],,
  ac_cv_cxx_stdcxx_98=yes, ac_cv_cxx_stdcxx_98=no)
  AC_LANG_RESTORE
  ])
  if test "$ac_cv_cxx_stdcxx_98" = yes; then
    AC_DEFINE(STDCXX_98_HEADERS,,[Define if ISO C++ 1998 header files are present. ])
  fi
])

Check for library coverage of the TR1 standard.

# AC_HEADER_STDCXX_TR1
AC_DEFUN([AC_HEADER_STDCXX_TR1], [
  AC_CACHE_CHECK(for ISO C++ TR1 include files,
  ac_cv_cxx_stdcxx_tr1,
  [AC_LANG_SAVE
  AC_LANG_CPLUSPLUS
  AC_TRY_COMPILE([
  #include <tr1/array>
  #include <tr1/ccomplex>
  #include <tr1/cctype>
  #include <tr1/cfenv>
  #include <tr1/cfloat>
  #include <tr1/cinttypes>
  #include <tr1/climits>
  #include <tr1/cmath>
  #include <tr1/complex>
  #include <tr1/cstdarg>
  #include <tr1/cstdbool>
  #include <tr1/cstdint>
  #include <tr1/cstdio>
  #include <tr1/cstdlib>
  #include <tr1/ctgmath>
  #include <tr1/ctime>
  #include <tr1/cwchar>
  #include <tr1/cwctype>
  #include <tr1/functional>
  #include <tr1/memory>
  #include <tr1/random>
  #include <tr1/regex>
  #include <tr1/tuple>
  #include <tr1/type_traits>
  #include <tr1/unordered_set>
  #include <tr1/unordered_map>
  #include <tr1/utility>
  ],,
  ac_cv_cxx_stdcxx_tr1=yes, ac_cv_cxx_stdcxx_tr1=no)
  AC_LANG_RESTORE
  ])
  if test "$ac_cv_cxx_stdcxx_tr1" = yes; then
    AC_DEFINE(STDCXX_TR1_HEADERS,,[Define if ISO C++ TR1 header files are present. ])
  fi
])

An alternative is to check just for specific TR1 includes, such as <unordered_map> and <unordered_set>.

# AC_HEADER_TR1_UNORDERED_MAP
AC_DEFUN([AC_HEADER_TR1_UNORDERED_MAP], [
  AC_CACHE_CHECK(for tr1/unordered_map,
  ac_cv_cxx_tr1_unordered_map,
  [AC_LANG_SAVE
  AC_LANG_CPLUSPLUS
  AC_TRY_COMPILE([#include <tr1/unordered_map>], [using std::tr1::unordered_map;],
  ac_cv_cxx_tr1_unordered_map=yes, ac_cv_cxx_tr1_unordered_map=no)
  AC_LANG_RESTORE
  ])
  if test "$ac_cv_cxx_tr1_unordered_map" = yes; then
    AC_DEFINE(HAVE_TR1_UNORDERED_MAP,,[Define if tr1/unordered_map is present. ])
  fi
])

# AC_HEADER_TR1_UNORDERED_SET
AC_DEFUN([AC_HEADER_TR1_UNORDERED_SET], [
  AC_CACHE_CHECK(for tr1/unordered_set,
  ac_cv_cxx_tr1_unordered_set,
  [AC_LANG_SAVE
  AC_LANG_CPLUSPLUS
  AC_TRY_COMPILE([#include <tr1/unordered_set>], [using std::tr1::unordered_set;],
  ac_cv_cxx_tr1_unordered_set=yes, ac_cv_cxx_tr1_unordered_set=no)
  AC_LANG_RESTORE
  ])
  if test "$ac_cv_cxx_tr1_unordered_set" = yes; then
    AC_DEFINE(HAVE_TR1_UNORDERED_SET,,[Define if tr1/unordered_set is present. ])
  fi
])

Check for baseline language coverage in the compiler for the C++11 standard.

# AC_COMPILE_STDCXX_11
AC_DEFUN([AC_COMPILE_STDCXX_11], [
  AC_CACHE_CHECK(if g++ supports C++11 features without additional flags,
  ac_cv_cxx_compile_cxx11_native,
  [AC_LANG_SAVE
  AC_LANG_CPLUSPLUS
  AC_TRY_COMPILE([
  template <typename T>
    struct check final
    {
      static constexpr T value{ __cplusplus };
    };

    typedef check<check<bool>> right_angle_brackets;

    int a;
    decltype(a) b;

    typedef check<int> check_type;
    check_type c{};
    check_type&& cr = static_cast<check_type&&>(c);

    static_assert(check_type::value == 201103L, "C++11 compiler");],,
  ac_cv_cxx_compile_cxx11_native=yes, ac_cv_cxx_compile_cxx11_native=no)
  AC_LANG_RESTORE
  ])

  AC_CACHE_CHECK(if g++ supports C++11 features with -std=c++11,
  ac_cv_cxx_compile_cxx11_cxx,
  [AC_LANG_SAVE
  AC_LANG_CPLUSPLUS
  ac_save_CXXFLAGS="$CXXFLAGS"
  CXXFLAGS="$CXXFLAGS -std=c++11"
  AC_TRY_COMPILE([
  template <typename T>
    struct check final
    {
      static constexpr T value{ __cplusplus };
    };

    typedef check<check<bool>> right_angle_brackets;

    int a;
    decltype(a) b;

    typedef check<int> check_type;
    check_type c{};
    check_type&& cr = static_cast<check_type&&>(c);

    static_assert(check_type::value == 201103L, "C++11 compiler");],,
  ac_cv_cxx_compile_cxx11_cxx=yes, ac_cv_cxx_compile_cxx11_cxx=no)
  CXXFLAGS="$ac_save_CXXFLAGS"
  AC_LANG_RESTORE
  ])

  AC_CACHE_CHECK(if g++ supports C++11 features with -std=gnu++11,
  ac_cv_cxx_compile_cxx11_gxx,
  [AC_LANG_SAVE
  AC_LANG_CPLUSPLUS
  ac_save_CXXFLAGS="$CXXFLAGS"
  CXXFLAGS="$CXXFLAGS -std=gnu++11"
  AC_TRY_COMPILE([
  template <typename T>
    struct check final
    {
      static constexpr T value{ __cplusplus };
    };

    typedef check<check<bool>> right_angle_brackets;

    int a;
    decltype(a) b;

    typedef check<int> check_type;
    check_type c{};
    check_type&& cr = static_cast<check_type&&>(c);

    static_assert(check_type::value == 201103L, "C++11 compiler");],,
  ac_cv_cxx_compile_cxx11_gxx=yes, ac_cv_cxx_compile_cxx11_gxx=no)
  CXXFLAGS="$ac_save_CXXFLAGS"
  AC_LANG_RESTORE
  ])

  if test "$ac_cv_cxx_compile_cxx11_native" = yes ||
     test "$ac_cv_cxx_compile_cxx11_cxx" = yes ||
     test "$ac_cv_cxx_compile_cxx11_gxx" = yes; then
    AC_DEFINE(HAVE_STDCXX_11,,[Define if g++ supports C++11 features. ])
  fi
])

Check for library coverage of the C++2011 standard. (Some library headers are commented out in this check, they are not currently provided by libstdc++).

# AC_HEADER_STDCXX_11
AC_DEFUN([AC_HEADER_STDCXX_11], [
  AC_CACHE_CHECK(for ISO C++11 include files,
  ac_cv_cxx_stdcxx_11,
  [AC_REQUIRE([AC_COMPILE_STDCXX_11])
  AC_LANG_SAVE
  AC_LANG_CPLUSPLUS
  ac_save_CXXFLAGS="$CXXFLAGS"
  CXXFLAGS="$CXXFLAGS -std=gnu++11"

  AC_TRY_COMPILE([
    #include <cassert>
    #include <ccomplex>
    #include <cctype>
    #include <cerrno>
    #include <cfenv>
    #include <cfloat>
    #include <cinttypes>
    #include <ciso646>
    #include <climits>
    #include <clocale>
    #include <cmath>
    #include <csetjmp>
    #include <csignal>
    #include <cstdalign>
    #include <cstdarg>
    #include <cstdbool>
    #include <cstddef>
    #include <cstdint>
    #include <cstdio>
    #include <cstdlib>
    #include <cstring>
    #include <ctgmath>
    #include <ctime>
    // #include <cuchar>
    #include <cwchar>
    #include <cwctype>

    #include <algorithm>
    #include <array>
    #include <atomic>
    #include <bitset>
    #include <chrono>
    // #include <codecvt>
    #include <complex>
    #include <condition_variable>
    #include <deque>
    #include <exception>
    #include <forward_list>
    #include <fstream>
    #include <functional>
    #include <future>
    #include <initializer_list>
    #include <iomanip>
    #include <ios>
    #include <iosfwd>
    #include <iostream>
    #include <istream>
    #include <iterator>
    #include <limits>
    #include <list>
    #include <locale>
    #include <map>
    #include <memory>
    #include <mutex>
    #include <new>
    #include <numeric>
    #include <ostream>
    #include <queue>
    #include <random>
    #include <ratio>
    #include <regex>
    #include <scoped_allocator>
    #include <set>
    #include <sstream>
    #include <stack>
    #include <stdexcept>
    #include <streambuf>
    #include <string>
    #include <system_error>
    #include <thread>
    #include <tuple>
    #include <typeindex>
    #include <typeinfo>
    #include <type_traits>
    #include <unordered_map>
    #include <unordered_set>
    #include <utility>
    #include <valarray>
    #include <vector>
  ],,
  ac_cv_cxx_stdcxx_11=yes, ac_cv_cxx_stdcxx_11=no)
  AC_LANG_RESTORE
  CXXFLAGS="$ac_save_CXXFLAGS"
  ])
  if test "$ac_cv_cxx_stdcxx_11" = yes; then
    AC_DEFINE(STDCXX_11_HEADERS,,[Define if ISO C++11 header files are present. ])
  fi
])

As is the case for TR1 support, these autoconf macros can be made for a finer-grained, per-header-file check. For <unordered_map>

# AC_HEADER_UNORDERED_MAP
AC_DEFUN([AC_HEADER_UNORDERED_MAP], [
  AC_CACHE_CHECK(for unordered_map,
  ac_cv_cxx_unordered_map,
  [AC_REQUIRE([AC_COMPILE_STDCXX_11])
  AC_LANG_SAVE
  AC_LANG_CPLUSPLUS
  ac_save_CXXFLAGS="$CXXFLAGS"
  CXXFLAGS="$CXXFLAGS -std=gnu++11"
  AC_TRY_COMPILE([#include <unordered_map>], [using std::unordered_map;],
  ac_cv_cxx_unordered_map=yes, ac_cv_cxx_unordered_map=no)
  CXXFLAGS="$ac_save_CXXFLAGS"
  AC_LANG_RESTORE
  ])
  if test "$ac_cv_cxx_unordered_map" = yes; then
    AC_DEFINE(HAVE_UNORDERED_MAP,,[Define if unordered_map is present. ])
  fi
])

# AC_HEADER_UNORDERED_SET
AC_DEFUN([AC_HEADER_UNORDERED_SET], [
  AC_CACHE_CHECK(for unordered_set,
  ac_cv_cxx_unordered_set,
  [AC_REQUIRE([AC_COMPILE_STDCXX_11])
  AC_LANG_SAVE
  AC_LANG_CPLUSPLUS
  ac_save_CXXFLAGS="$CXXFLAGS"
  CXXFLAGS="$CXXFLAGS -std=gnu++11"
  AC_TRY_COMPILE([#include <unordered_set>], [using std::unordered_set;],
  ac_cv_cxx_unordered_set=yes, ac_cv_cxx_unordered_set=no)
  CXXFLAGS="$ac_save_CXXFLAGS"
  AC_LANG_RESTORE
  ])
  if test "$ac_cv_cxx_unordered_set" = yes; then
    AC_DEFINE(HAVE_UNORDERED_SET,,[Define if unordered_set is present. ])
  fi
])

Some C++11 features first appeared in GCC 4.3 and could be enabled by -std=c++0x and -std=gnu++0x for GCC releases which pre-date the 2011 standard. Those C++11 features and GCC's support for them were still changing until the 2011 standard was finished, but the autoconf checks above could be extended to test for incomplete C++11 support with -std=c++0x and -std=gnu++0x.

This is a change in behavior from older versions. Now, most iterator_type typedefs in container classes are POD objects, not value_type pointers.